POS0040 SILENCING OF JOINT FIBROBLAST TO PROTECT FROM JOINT DAMAGE
Authors: S. Rauber, H. Mohammadian, M. G. Raimondo, M. Vogg, L. Lu, A. Soare, C. Xu, J. D. D. Cañete, G. Schett, A. Ramming
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Despite significant progress in the development of targeted biologic therapies for the treatment of chronic inflammatory joint diseases such as rheumatoid arthritis or psoriatic arthritis, more than 40% of patients still record gradual loss of joint function, mostly because of failure to archive complete remission. Herein, persistent joint fibroblast activity leads to continuous destruction of the joint, whereas its inhibition/silencing prevents joint damage despite presence of a residual inflammation<sup>[1]</sup>. Persistent activation of the joint fibroblasts leads to destruction of the joint<sup>[1]</sup>, and silencing both, inflammation and mesenchymal activation is required to protect joints from damage. <h3>Objectives</h3> Protection from joint damage-especially when complete remission cannot be achieved-is a need that might be met by pharmacological targeting of fibroblasts. We aimed to reprogram fibroblasts, from pro-inflammatory and tissue damaging phenotype to a tissue preserving and anti-inflammatory phenotype as a new promising treatment strategy. <h3>Methods</h3> Single-cell RNA sequencing of sorted synovial fibroblasts and imaging mass cytometry from different mouse models of arthritis (TNFtg, <i>Il23</i> overexpression, KBxN serum transfer) were used to map fibroblast heterogeneity. Co-culture experiments were performed with sorted fibroblasts and innate lymphoid cells (ILCs) <i>in vitro</i>. For functional proof of concept, animals were treated with blocking and activating antibodies in the aforementioned arthritis models. Validation in human synovial biopsies by imaging mass cytometry and spatial transcriptomics was performed. <h3>Results</h3> Through data analysis of joint fibroblast scRNAseq, spatial transcriptomics, and imaging mass cytometry during joint inflammation and its resolution, we observed high plasticity of joint fibroblast populations. By analyzing single-cell dynamics, we identified transdifferentiation of fibroblasts from a MMP3+/IL-6+ destructive state to a DKK3+ protective phenotype upon DMARD-induced resolution and revealed the underlying molecular processes. We identified a novel DKK3+ fibroblast subtype in joints of patients with rheumatoid arthritis and spondyloarthritis (axial spondyloarthritis, peripheral spondyloarthritis, psoriatic arthritis) that protects against joint damage and actively induces resolution of inflammation, by stimulating type 2 ILCs, which are known cellular components for activation of regulatory T cells and pro-resolving eosinophil granulocytes in the joint<sup>[2]</sup>. We identified the functionally relevant pathway of type 2 IlC activation by fibroblasts. Drug-induced activation of this pathway resulted in activation of pro-resolving ILC2s/Tregs/eosinophil granulocytes in association with a sharp decrease in inflammation and cartilage and bone destruction. <h3>Conclusion</h3> This new treatment approach might have several advantages over anti-inflammatory drugs. (i) no interference with important defence mechanisms against pathogens and no increased risk of opportunistic infections, (ii) activation of a mechanism that retains tissue integrity, (iii) option to combine with anti-inflammatory drugs, making silencing of fibroblasts to a new tool of disease control. <h3>References</h3> [1]Croft, A.P., et al. Distinct fibroblast subsets drive inflammation and damage in arthritis. <i>Nature</i> 570, 246-251 (2019). [2]Rauber, S., et al. Resolution of inflame mation by interleukin-9-producing type 2 innate lymphoid cells. <i>Nat Med</i> 23, 938-944 (2017). <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.